We have generated our repump frequency for a MOT by injection-locking to a sideband at roughly 6.8 GHz. This is something that we have done for some time; however, we have implemented a new method to generate the RF frequency.

For the past so many years, we have been using a Mini-Circuits VCO to generate the RF frequency. It is good but not great. It involves a lot of calibration and tuning. Cleaning this up and making it easier to use has been a large part of Paul Russell’s undergraduate research project. Today, Mara Klebonas and I (Paul will be back tomorrow), set up our new digital RF generator, SG12000PRO PureSine Generator. We use one minicircuits amp and then directly to the phase modulator. It works beautifully!

In the image above is the sidebands that was generated by the sinewave generate. Ignoring the sideband on the right, the side bands from left to right are -1, +2, 0th, -2, +1. Its tricky to see this but it has to due with our Fabry-Perot Cavity having a FSR of 1.5 GHz.

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We use injection-locking to filter out all but one of the side bands. Shown below is the spectrum of our injection-lock laser (and a picture of Mara). The injection current is also shown here.

So here was the trick. We had been locking the injection-locked laser at a temperature of 23 C. The laser was nicely optimized for injection locking. However, because it was too nicely optimized, the filtering of the sidebands wasn’t very effective. It locked too much of the signal. So we made the injection-locked system worse by tuning the temperature to 14C. The scanning range was reduced some but the filtering works great and the system appears to be stable.

FUN STUFF!